Tunable magnetron



Sept. 24, 1946Ao P. if. SPENCER 2,408,234 v TUNABLE MAGNETRON Filed Nov. 26, 1941 Inlvez'zaw fel .3 I @8g4 Patented Sept. 24,1946 A UNITED STATES I .y 2,408,234 i 1* yjjj.' fi .fgjf l TUNABLE MAGNETRON y n' f Y`VPercy L. Spencer, West Newton, Mass., assignor,by 'y mesne assignments, to Raytheon.Manufactur.v f ing Company, a corporation of .Delaware 'Y Application November 26, 1941, Serial No. 420,558 14 claims.k .(01.250-2'15Y invention relates to-,a magnetron. and more particularly to a magnetron inV which the dimensions of the internal Vstructure determine thefrequency of the oscillations produced.

VIn magnetrons of this kind it is diicult to construct the component parts thereof t6 dimensions which will produce a desired frequency within narrow limits, particularly when the oscillations Vproduced are of extremely short wave length,.of the order of centimeters. Therefore, it isidesirable that some simple arrangement be devised for tuning the' magnetron after it has been completed to bring its frequency of oscillation to an exact predetermined value even though, as originally constructed, said frequency may deviate somewhat from said desired predetermined value.

An object of this invention is to devisea magnetron'of the foregoing type in which-simple but effective tuning means are provided. v e

Another object lof 'this invention is to'devise a magnetron ofl the foregoingV type which is simplevin construction and. yet rugged enough to withstand severe usage.:

. .The foregoing` and other objects Will be Vbest understood from the following description of exemplications thereof.; reference being had .toV

the accompanying dra wing,'wherein-:

Fig. 1 isa vertical cross-sectionthrough a magnetron incorporating my invention, taken along Fig. 2 is a cross-section taken along line 2-2 of Fig. 1; and

Fig. 3 is a fragmentary perspective viewof anotherlmodieation of my invention.

:In the embodiment illustrated in Figs. 1 and l2, themagnetron comprises an envelope I which is preferably made of a blockof conductive material, such as copper.k 'Ihis vblock forms the anode ofthe magnetron.v Said block has hollow end sections which are covered by end caps 2 and 3 likewise of conductive material,l such as copper. Between the hollow end sections of the block I is. the central bridging portion 4. The portion 4 is provided with a central bore 5 within which is supported substantially at the center thereof aA cathode 6 of the thermionic type. The cathode y issupported by a pair of cathode'lead-in conductors 4'l4 and 8 sealed through glass seals Sand I0 mounted at the outer ends of pipes II and I2A hermetically fastened Within the walls of the block I adjacent the upper and lower hollow end sections. A plurality of slots I3 extendradially from the central bore 5- to within a short distance gf the outer Wall of the block I.

.rA capacity exists between thecathode 6 and each of the wedge-shaped sections of they bridging portion 4. Also capacitances exist between the sidewalls of each .of the slots I3. The Walls of the slots I3 likewise form 'inductances f The anode, therefore, may be so designed and so spaced relative tothe cathode that the inductances and capacitances described will constitute circuits which are tuned,.and thus resonant at substantially the frequency at which the device istobe operated. f

- When such a magnetron is placedbetween suitable magnetic poles I4 and I5 to create a longi` tudinal magnetic field and the device is energized, oscillations, are set up whose frequency and con' sequently whose wave length are determined primarily by the dimensions of each of the slots I3 as describedrabove. The oscillations produced in these slots reinforce each other, and may be led out from the tube by means Aof a coupling conductor I6 fastened to the central bridgeV portion 4 near the central bore 5 between two of the slots I3. The coupling conductor I6 leads out from the magnetron through a glass seal rI8 at the outer end of a pipe I1 likewise hermetically fastened through the wall of the envelope I adjacent the upper hollow portion thereof. An additional conducting pipe'llv may be fastened to the pipel I1 outside of the seal I8 so as to form with the coupling conductor I6 a concentric line through which the high frequency oscillations generated by the magnetron may be conducted away and utilized. Y

,Such a magnetron as I have described may be constructed so as to produce oscillations having found that the provision of lsuch a slot decreasesthe frequency of the oscillations generated by the magnetron to van'appreciable degree. The effect seemsl to Vbe that cutting' this slot increases the inductance of each of the oscillating loops within the magnetron. This feature in itselfrpro- Vides a convenientwayof adjusting the frequency .of a magnetron` after the central bore 5 and the` slots I3 have been cut. y Y

I havealso foundthat if a ring 20 of a conducting material such Vas copper isintroduc ed into said slot I9, the frequency of the oscillations produced is increased. The introduction of the ring seems to have the effect of decreasing the inductance of each of the oscillating loops within the magnetron, and thus causing a higher frequency to be generated. The ring 20 is supported on a rather stiff conducting rod 2|, the outer end of which is secured to the inner wall of a conducting' pipe 22 likewise hermetically fastened in the wall of the envelope I adjacent the upper hollow portion thereof. The outer end of the pipe 22 may have sealed thereon a glass bulb 23 within which may be Contained some gettering material 24. During evacuationof the tube, thel getter 24 may be ashed by inductive heating to clean up residual gases within the magnetron.

When the magnetron has been completed, it is placed between the magnetic poles I4 and I5 and connected into a suitable oscillating circuit. The

Wave length of the oscillations generated is then measured. 1f it is found that the wave length so generated deviates from the exact value desired, themagnetron may be tuned to that exact frequency by bending .the tube 22 so as to move the rod 2l, thus raising or lowering the ring 20. The tube Z2 is of the proper stiffness so that when bent into any position, it remains nxed in that position. I have found, for example, that in one size magnetron, the range through which the device could be tuned represented a change of wave lengths from 3.2 to 3.5 centimeters. This is an ample range of variation for all practical purposes in order to bring such a device into exact tuning with thefreduency which the device is intended to generate.

Instead or constructing the magnetron with straight-sided slots I3, the inductance of the oscillating section of the magnetron may be increasedv as shown in Fig. 3. In this ligure the same reference numerals are applied where the elementsare identical with those shown inFigs. 1 and 2. in this embodiment the outer-ends oi the slots i3 terminate in cylindrical openings 25, thus causing the magnetron to generate longer wavelengths. The magnetron is provided :with a ring 28 similar to the ring 20`in the embodiment of Figs. 1 and 2, but carrying conducting plugs 2S of some suitable material, such as copper. The plugs 2e are located opposite the ends of the openings 2-5 so that they may be caused to project' into the ends of said holes to any predetermined extent. The adjustment of the position of the plugs 2S performs substantially the same tuning action as described above in connection with the adjustment of the position of the ring 2c.' As the plugs 2% project further into the openings 25, the inductance of the oscillating `sections of the magnetron decreases, while moving -said plugs away from the openings increases said inductance.` f

Of course it is to be understood thatt-his `invention is not limited to the particular details as descri-bedabove as many equivalents will suggest themselves to those skilled in the art; It is accordingly desired that the appended claims be given a broad interpretation commensurate `with the scope oi the invention within the art.

What is claimed is: i'

l. An electron dischargev device comprising a cathode, an anode disposed adjacent said cathode, said anode having electronreceiving portions ad-4 jacent said cathode, anda plurali-ty of'g-rooved portions spaced from said nrst portions forming inductances which together with thev interelectrode capacitances constitute a tuned circuit, said anode having cut-away localized portions in said grooved portions providing localized sections of said grooved portions, each of said localized grooved portions having a length differing from the rest of the respective grooved portion for predetermining the inductances of said grooved portions, and a conductive member supported adjacent said cut-away portions.

2. An electron discharge' device comprising a cathode, an anode disposed adjacent said cathode, said anode having electron-receiving portions adjacent said cathode, and a plurality of grooved portions spaced from said rst portions forming inductances which together with the interelectrode eapacitances constitute a tuned circuit, said anode having cut-away localized portions in said grooved portions providing localized sections of said grooved portions, each of said localized grooved portions having a length differing from the rest of the respective grooved por-7 tion for predetermining .the inductances of said grooved portions, `and a conductive member supported adjacent said cut-away portions, said conductive member being adjustable toward and away from said cut-away portions to vary said inductances.

3. An electron discharge device comprising an electrode having .arms bounding a cavity and forming an inductance, said arms having juxtaposed surfaces forming a capacitance, another electrode adjacent the outer ends of said arms, one of said arms having a cut-away localized portion for predetermining said inductance, and a conductive member supported adjacent said cutawayl portion, said conductive member vbeing adjustable toward and away from said cut-away portion to vary said inductance.

s. A magnetron comprising an anode having arms bounding a, cavity and forming an inductance, said arms having juxtaposed surfaces forming ka capacitance, a cathode adjacent 'the outer ends of said arms, means for producing a magnetic-field about said cathode, one of said arms having a cut-away localized portion for predetermining said inductance, and aV conductive member supported adjacent f to and spaced from said cut-away portion, said conductive member being adjustable toward and away from said cut-away portion tovary said inductance.

5. An electron discharge device comprising a cathode, an anode structure, said anode structure comprising a body of conducting material having substantially nat upper and lower faces parallel with each other, said body having a pair of electron-(receiving portions extending between said faces and disposed adjacent said cathode, said body also having a groove extending from between said electron-receiving port-ions* and likewise extending from one ofgaid faces-tothe other, said groove forming a cavity resonator having capacity and inductance constituting a tuned circuit, said anode having a cut-away localized'portion in one of said faces at a portion of said groove providing a localized section of said groove having a length differing from the restrof said groove for predetermining the inductance of said cavity resonator, and 4a conductive member supported adjacent said cutaway portion,`said conductive member being adjustable toward and away from said groove to vary said inductance. Y

6. A magnetronY comprising a cathode, means adjacent said cathode for producing a magnetic iield about said cathode, an anode structure,said anode structure comprising ay body of conducting material having substantially flat upper and lower faces parallel with each other, said body having a plurality of pairs of electron-receiving portions extending between said faces and disposed adjacent said cathode, said body also having a plurality of grooves extending from between said electron-receiving portions and likewise extending from one of said faces to the other, each of said grooves forming a cavity resonator having capacity and inductance constituting a tuned circuit, said anode having cut-away localized portions in one of said faces at a portion of each of said grooves providing localized sections of said grooves, each having a length differing from the rest of said grooves for predetermining the inductances of said cavity resonators, and a conductive member supported adjacent each of said cut-away portions.

7. An electron discharge device comprising a sealed envelope containing an elongated cathode, an anode structure having adjacent anode elements defining a transverse cavity resonator, an adjustable tuning element within said envelope adjacent said cavity resonator, said tuning element comprising a conductive member, and means connected to said tuning element for adjusting the position of said conductive member toward and away from said cavity resonator.

8. A magnetron comprising a cathode surrounded by an anode block, said block having a central cathode space and interconnecting spaces forming coupled cavity resonators,said block also having a pair of anode arms forming opposite sides of each of said cavity resonators,

' an adjustable tuning element within said envelope adjacent said cavity resonators, said tuning element comprising a conductive member, and means connected to said tuning element for adjusting the position of said conductive member toward and away from said cavity resonators.

9. An electron discharge device comprising a sealed envelope containing an elongated cathode, an anode structurerhaving adjacent anode elements 'deiining a transverse cavity resonator, an adjustable tuning element within said envelope adjacent said cavity resonator, said tuning element comprising a conductive member, and means operable externally of said envelope and connected to said tuning element for adjusting the position of said conductive member toward and away from said cavity resonator.

10. A magnetron comprising a cathode surrounded byY an anode block, said block having a central cathode space and interconnecting spaces forming coupled cavity resonators, said block also having a pair of anode arms forming opposite sides of each of said cavity resonators, an adjustable tuning element within said envelope adjacent said cavity resonators, said tuning element comprising a conductive member, and means operable externally of said envelope and connected to said tuning element for adjusting the position of said conductive member toward and away from said cavity resonators.

11. An electron discharge device comprising a sealed envelope containing an elongated cathode, an anode structure having adjacent anode elements dening a transverse cavity resonator, an adjustable tuningelement within said envelope adjacent said cavity resonator, said tuning element having a conductive element projecting into said cavity resonator, and means connected to said tuning element for adjusting the position of said conductive member toward and away from said cavity resonator.

12. A magnetron comprising a cathode surrounded by an anode block, said block having a central cathode space and interconnecting spaces forming coupled cavity resonators, said block also having a pair of anode arms forming opposite sides of each of said cavity resonators, an

' adjustable tuning element within said envelope adjacent said cavity resonators, said tuning element having conductive elements projecting into said cavity resonators, and means connected to said tuning element for adjusting the position of said conductive member toward and away fromA f rounded by an anode block, said block having a central cathode space and interconnecting spaces forming coupled cavityv resonators, said block also having a pair lof anode arms forming opposite sides of each ofsaid cavity resonators, said anode arms having cut-away portions disposed intermediate the ends of said anode arms providing each of said anode arms with a longitudinal dimension at said cut-away portion less than the longitudinal dimension of the rest of said anode arm'.

14. An electron discharge device comprising ay v formable tube sealed to and extending beyond said envelope whereby the position of said conductive member may be adjusted by deforming said tube.

PERCY L. SPENCER. 

